Simulation of earthquake : Study of a 3 concrete packages stack stability

As part of the safety analysis relating to storage facilities or storage of hazardous materials performed for Andra, it is necessary to estimate the consequences of an earthquake on sensitive equipment.

The issue approached here concerns the study of the stability of a stack of three concrete storage package, based on a transfer trolley that moves on rails.

It is a question of determining the situations which can bring potentially to the fall of one or some storage package, when the carriage is subject, at the link between wheel and rail, to a harmonic excitation from either a lack of geometric civil engineering or a spectrum of an earthquake.

During the accidental event, two parameters are to be taken into account: the signal amplification brought to the initial signal by the trolley, and the description of multiple contacts between the packages under the vibrations, able to change the arrangement of the stack. The contacts are not managed in the linear analyses of static or spectral type. The use of an explicit nonlinear time simulation was adopted.

The unique common mesh for both simulations (RADIOSS Block and OptiStruct) of the trolley and the package storage has been realized thanks to HyperMesh software of HyperWorks suite.

In a first step, the modes of the transfer trolley equipped with its stack modeled by an added mass are determined using modal analysis conducted with RADIOSS Bulk. The specific mode that involves the most weight and the frequency which is included in the bandwidth of the spectrum of an earthquake or fault geometry is retained.

The second step is conducted under RADIOSS Block. The three packages of stack and trolley are modeled. The contacts are taken into account. The first simulation launched corresponds to a large roll of the trolley: an excitation signal is imposed on its wheels, with a phase displacement between the left and right rails.

In modal analysis, the roll Eigen modes type was privileged. An Eigen mode with a frequency in the bandwidth 0-34 Hz and with a participating mass of about 80% of the total mass is selected.
The time harmonic signal is fed back at the level of rails in the RADIOSS Block model. A sensitivity study was led on the amplitudes needed for the destabilization of the storage stack. Modeled durations are on the order of 12 s with a model of 200,000 elements.

Conclusions and perspectives:
Other excitation types are later planned. It would be interesting to set up an experimental plan whose variables are the package type, the height of the stack and the nature of the excitation. The restitution times of calculations are long. We need to find a compromise between simplicity of models and scope of the response surface.

The Author

Eric TOGNI and Sylvain Tholance
119, Boulevard STALINGRAD

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